Tracing spatial and temporal dynamics of post-fire sediment transport and redistribution using multiple rare earth element tracers: Insights into grassland management

Authors: BURGER, WILLIAM - Temple University; Van Pelt, Robert - Scott; GRANDSTAFF, DAVID - Temple University; WANG, GUAN - Beijing Forestry University; SANKEY, TEMUULEN - Northern Arizona University; LI, JUNRAN - University Of Hong Kong; SANKEY, JOEL - Us Geological Survey (USGS); RAVI, SUJITH - Temple University

Submitted to: Earth Surface Processes and Landforms
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/20/2023
Publication Date: 11/11/2023
Citation: Burger, W., Van Pelt, R.S., Grandstaff, D., Wang, G., Sankey, T.T., Li, J., Sankey, J.B., Ravi, S. 2023. Tracing spatial and temporal dynamics of post-fire sediment transport and redistribution using multiple rare earth element tracers: Insights into grassland management. Earth Surface Processes and Landforms. 128(11). https://doi.org/10.1029/2023JF007274.
DOI: https://doi.org/10.1029/2023JF007274

Interpretive Summary: In the southwestern United States and other semi-arid and arid regions of the world, grasslands are being invaded and replaced by shrubby vegetation communities that are less productive. The reason for this vegetation shift is uncertain, but may be mitigated or reversed by management. University and U.S. federal agency scientists collaborated with U.S. Fish and Wildlife Service employees at the Sevilleta National Wildlife Reserve to test Rare Earth Element (REE) Tracers applied to soils under different vegetation types in a shrub and grassland transition zone. Half of the plots on which REE tracers were applied were burned and the sediment transport was monitored and analyzed for REE tracers following the fires. This paper represents the follow-up measurement of vegetation at the experimental sites to determine the effects of the fire on vegetation communiities and the effects of sediment redistribution on hose changes.

Technical Abstract: Many grasslands in arid and semi-arid regions are undergoing rapid changes in vegetation, including encroachment of woody plants and invasive grasses, which can alter the rates and patterns of fire and sediment transport in these landscapes. We investigated the spatial distribution of sediments at the scale of vegetated microsites for three years following a prescribed fire using a multiple rare earth element (REE) tracer-based approach in a shrub-grass transition zone in the northern Chihuahuan desert (New Mexico, USA). To this end, we applied REE tracers – holmium, europium, and ytterbium on shrub, grass, and bare microsites, respectively and collected soil and airborne samples. Results indicate that although the horizontal mass flux (HMF) of wind-borne sediment increased approximately threefold in the first windy season following the fire, and the HMF of both plots were not significantly different after three windy seasons. Comparing REE concentrations in sediments from both plots over the three years and three annual windy seasons, we observed a post-fire shift in source and sink dynamics of sediments. The tracer analysis of wind-borne sediments indicated that the source of the HMF in the burned site was mostly derived from shrub microsites following the fire, whereas the bare microsites were the major contributors for aeolian sediment in control areas. The shift in sources and sinks, and the spatial homogenization of REEs indicate that the removal of shrub vegetation resulted in sediment redistribution to the bare microsites even three years after the prescribed fire. The findings of this study will improve our understanding of post-fire geomorphic processes at a microsite scale in a grassland ecosystem undergoing land degradation induced by shrub encroachment.